FIG. 19 shows an example of conventional LED module (see e.g. Patent Document 1). The LED module X illustrated in the figure includes a case 91, a sub-mount substrate 92, a wising pattern 93, an LED chip 94 and a light-transmitting portion 95. The case 91 is made of e.g. resin. The sub-mount substrate 92 is made of e.g. Si. The wiring pattern 93 is formed on the sub-mount substrate 92 and has an obverse surface made of e.g. Au or Ag. The LED chip 94 is the light source of the LED module X and emits light of a predetermined wavelength. The LED chip 94 is mounted to the sub-mount substrate 92 by eutectic bonding to the wiring pattern 93. The light-transmitting portion 95 is made of a material that transmits light from the LED chip 94, such as silicone resin, and covers the LED chip 94.
After long use of the LED module X, the material such as Ag that forms the obverse surface of the wiring pattern 93 is corroded and changes to a dark color. The wiring pattern 93 that has changed to a dark color in this way absorbs light emitted from the LED chip 94. Thus, the amount of light emission from the LED module X may reduce with time.
Patent Document 1: JP-A-2006-237141